Spinning of acrylonitrile polymer fibers



Oct. 29, 1957 J. w. CLAPP ETAL 2,811,409

SPINNING OF ACRYLONITRILE POLYMER FIBERS 2 Sheets-Sheet 1 Filed Dec. 31, 1952 AIR PRESSURE METERING PUMP w W W. M D T w W M M067 T M U M W mwm EC WC. fl 4 "2U N00 U MO N.- m 0 m0 mo H mm mm l 1m .1... H2 0 m 4 mm 0 Mk 2 M H5 ME 2 J 2 a I I I IF er /50-400c 35 HOTAIR/NLET All? ourzr 7 I 3 6 a N NM T W 7 m 5 w Hw M H m HE R MW m M N L 0 F H r u T o u 0 0 a P 0 m 5 I JACKET HEAT/N6 FLU/D OUTLET HOTA/R INLET 250 4 00 C as m mm m wnw m a wm a MM MRJC A M4 a mm MW m DRAW ROL L8 47 1957 J. w. CLAPP ETAL 2,81

SPINNING OF ACRYLQNITRILEI POLYMER FIBERS 2 Sheets-Sheet 2 Filed Dec.

JAG/(ETHEAT/NG FLU/D INLET 250 400 C HOT AIR INZ E T 250' 400 C HEATED SHOES HEATED ROL LS ORA W ROLLS PP Q! INVEN TORS M 5 BY AUORNE )6 lh wm 5 Ma n r Mm JC 70 PAC/(AGE United States Patent SPINNING 0F ACRYLONITRILE POLYMER FIBERS John William Clapp and Charles B. Mather, Kingsport, Tenm, assignors to Eastman Kodak Company, Rocir ester, N. Y., a corporation of New Jersey Application December 31, 1952, Serial No. 328,894

4 Claims. (Cl. 1854) This invention relates to the spinning of synthetic filaments from solutions of polyacrylonitrile or from solutions of graft or place polymers of polyacrylonitrile that are modified by one or more compounds which impart improved dye afiinity and moisture absorption to the filaments. More particularly the invention relates to the dry spinning of such polymers into filaments under carefully controlled dry spinning conditions, as well as to a continuous process for dry spinning, drafting and relaxing such filaments to produce a superior yarn product.

An object of the present invention is to produce improved filaments of polyacrylonitrile or modified polyacrylonitrile useful in the textile arts. Another object is to produce polyacrylonitrile or modified polyacrylonitrile by an evaporative process at high production rates. A further object is to produce polyacrylonitrile or modified polyacrylonitrile fibers having a sufiiciently low residual solvent content to permit immediate drafting and/ or relaxation of the fibers without further processing to remove residual solvent. A still further object of the invention is to produce filaments of high elongation and tenacity from solutions of such acrylonitrile polymers. Yet another object of the invention is to produce fibers of negligible boiling water shrinkage from solutions of polyacrylonitrile or modified polyacrylonitrile. Another object is to produce, if desired, yarns having relatively high diameters in the finished drafted and relaxed state. Other objects will appear hereinafter.

In accordance with the invention these and other objects are accomplished by a process and apparatus which may be described in connection with the accompanying detailed description and drawings in which Fig. 1 schematically discloses a source of spinning solution, a metering pump, filters and heaters for the solution, a dry spinning cabinet, and various stretching and relaxing rolls for continuously producing filaments having superior physical and chemical characteristics; and Fig. 2 schematically discloses a modification of the stretching and relaxing apparatus.

Referring to Fig. 1 of the drawings, there is disclosed apparatus in accordance with the invention in which air under pressure from a source, not shown, is introduced through pipe 10 into blow case 11 which contains the spinning solution 12 and forces the solution into pipe 13 which connects in series metering pump 14, filter 15, heated tube 16 and spinneret 18, the latter being positioned in spinning cell 20. A heating jacket 17 which may be heated in any suitable manner is associated with spinneret 18. As clear in the drawing, the spinning cell 20 comprises an elongated cylindrical structure having three separately operated heat jackets 21, 22 and 23 on the outside thereof. Each heating jacket has the usual fluid inlet and outlet pipes associated therewith as shown by the legend on the drawing. It is apparent that they each are adapted to heat approximately one-third of the surface of cell 20. The filaments 19 leaving spinneret 18 are conducted downwardly through the drying chambar 24 of the spinning cell 20 and thence through aperevaporation of solvent.

2,811,409 Patented Oct. 29, 1957 "ice ture 25 in the end of the spinning cell to a draw roll 41 and idler cot 42 and thence to other elements of the apparatus as is described later in this specification.

As indicated by the previous description of the three separately operated heating jackets 21, 22 and 23, the temperature of the drying atmosphere Within drying chamber 24 may be controlled along the approximate cncthird sections adjacent the three heating jackets.

However, the conditioning of the filaments is also facilitated by the introduction of heated air into the spinning chamber 24 at several points along the travel of the filaments. The air introduced into drying chamber 2 may also be removed from the chamber at several points. The apparatus may be operated while using some or all of the air inlets and outlets as will be described hereinafter.

Since heated air tends to rise upwardly through the spinning cell drying chamber 24, the description of the control of heated air into the cell 20 will commence at the lowest point of introduction which is above aperture through which the dried filaments leave the bottom of the spinning cell.

As shown in Fig. 1, heated air is introduced near the base of the cell 20 through diametrically opposite pipes 26 and 27. A portion of this air entering through pipes 26 and 27 may leave cell chamber 24 through diametrically oppositely positioned pipes 28 and 29. Additional heated air is introduced into cell chamber 24 through pipes 31 and 32, and a portion of this air may leave the cell chamber 24 through pipes 33 and 34.

Heated air is also blown across the filaments adjacent the spinneret 18 through pipe 35 and nozzle 36. The stream of air from the nozzle 36 is directed on the filaments just below the spinneret to increase the initial The nozzle 36 may be of any convenient shape as long as it directs a relatively high velocity of air onto the filaments. It appears improved filaments result at this point in the process because there is great evaporation at lower temperatures and over a relatively short length of the filaments as contrasted to subsequent evaporation over the length of the drying chamber. The temperature of the air blown across the face of the spinneret may be in certain instances considerably below or considerably above the boiling point of the volatile solvent of the spinning solution, for instance, plus or minus to 300 C. The volume of the air forced through the nozzle 36 may vary within limits of practicability, depending on the nature of the solvent, the extrusion rate and the flexibility of the filaments being extruded. Such variations are shown hereinafter. Air may leave the upper portion of the spinning chamber 24 through diametrically opposite pipes 37 and 38.

The spinning solution 12 is heated before being passed to the spinneret first in the candle type filter 15 preferably to a temperature of C. to C. and secondly in the small heating tube 16 which provides maximum heating surface with minimum volume for retention of the spinning solution. in this tube the solution is brought to the desired extrusion temperature which normally lies in the range of C. to C. when using dimethyl formamide as a solvent. The spinneret 18 is preferably made of stainless steel having a plurality of orifices. These orifices may vary in size from 0.04 mm. to 0.40 mm. in diameter, depending on the size of filaments desired. The spinneret assembly is jacketed with a heating jacket 17 which may be conventionally heated by a heating fluid such as hot oil or steam so as to maintain the temperature of the spinneret at the desired spinning temperature.

Referring to the legends on the drawing, Fig. 1, it will be seen heated air at temperatures corresponding to adjacent cell wall temperatures can be circulated through the spinning cell to remove the solvent from the filaments. The cell walls in the upper third portion may be maintained in a range of 70 C. to 200 C., in the center third portion 150 C. to 300 C., and in the lower third portion 250 C. to 400 C. Air heated to corresponding cell wall temperatures is admitted through pipes 26 and 27, and 31 and 32. In order to permit use of solutions having a relatively low viscosity and yet attain high spinning rates, a jet of hot air is blown through pipe 35 and jet 36 directly across the spinneret face to aid in the initial formation of the filaments. However, hot air above or below the temperature of the corresponding adjacent heating jackets can be employed in certain cases.

In a simple operation, yarn may be withdrawn directly from the bottom of the spinning cell 20 by rolls 41 and 42 and passed around a godet roll 47 and wound directly on a package, not shown, in a conventional manner.

However, when spinning large diameter filaments, it is advantageous to pass the yarn from the bottom of the spinning cell 20 and rolls 41 and 42 to a heated roll 43 where it becomes thermoplastic, the yarn being withdrawn from the heated roll 43 at a higher rate resulting in a drafting of the yarn before winding onto a package. This drafting method has the advantage of reducing the diameter and stiffness of the fibers and increasing their tenacity which renders them more easily handled. In this operation which can be followed by referring to Fig. 1, the filaments 19 will be passed around draw out roll 41 and between roll 41 and idler roll 42 and thence to and around hot roll 43 a desired number of times where the yarn is heated to a desired temperature by the hot roll and the associated heated shoe 44 which is positioned close to but out of contact with roll 43. Hot roll 43 and heated shoe 44 may be heated by any conventional means such as by hot oil, gas flames, or electricity. From roll 43 the heated, thermoplastic yarn progresses to the pair of draw rolls 45 and 46 which are rotated approximately at the same rate but also with an increase in peripheral speed over that of hot roll 43 to impart the desired stretch to the hot thermoplastic yarn. The yarn is passed several times around the pair of rolls 45 and 46 until sufficiently cool to permit winding in a package at which time it is passed around godet roll 47 and thence to a conventional packaging device, not shown. This drafting method has the advantage of reducing the diameter and stiffness of the fibers and increasing their tenacity which permits the fibers to be more easily handled.

Referring to Fig. 2 there is shown a modification of the stretching and relaxing apparatus which may be employed to process newly spun continuous yarn as it leaves the spinning cell 20. In Fig. 2 a broken away portion of the same dry spinning cell 20 of Fig. l is shown having heating jacket 23 which may be heated to 250400 C. and cell chamber 24 having air inlet pipes 26 and 27 through which air at 250400 C. may be introduced to dry the filaments 19 in the cell chamber 24. It will be understood that the spinning cell. is generally operated as described in connection with Fig. 1, the yarn leaving the cell through aperture 25. The yarn then passes partly around roll 41 and between 41 and 42 to heated roll 50 where it is heated to a desired temperature by the hot roll 50 and the associated heated shoe 51. From hot roll 50 the heated thermoplastic yarn progresses to the first pair of draw rolls 52 and 53 which are mutually rotated approximately the same rate but also with an increase in peripheral speed over that of roll 50 to impart the desired stretch to the hot thermoplastic yarn. The draw rolls 52 and 53 may, if desired, be internally heated to a temperature intermediate of that of the room and hot roll 50 to prevent too severe chilling of the yarn. Preferably rolls 52 and 53 (as well as rolls 56 and 57) are skewed in relation to each other so that the yarn may pass around the pair of them several times without tracking. This causes a snubbing action on the yarn and permits uniform tension control on the hot yarn along the length identified as A and also along the portion of the yarn identified as B. From roll 53 the yarn continues to heated relaxing roll 54 where it is heated by that roll and associated shoe 55. Relaxing roll 54 rotates at a lesser rate than do rolls 52 and 53 thereby permitting the hot, stretched yarn to relax. This relaxation takes place on the yarn at portions B as well as at portion C. The latter relaxation i permitted by running the second pair of draw rolls 56 and 57 at a slower peripheral speed than roll 55. Rolls 56 and 57 are rotated at the same speed. The yarn is also passed around rolls 56 and 57 several times to provide a snubbing action and control the tension of the yarn passing to the godet roll 58 from which the yarn is wound on a package by conventional means.

The present invention is further illustrated in the following examples:

Example 1 A spinning solution was prepared consisting of 19% of an acrylonitrile polymer, with an average molecular weight of 50,700 dissolved in dimethyl formamide to give a solution having a viscosity of 1020 poises at C. This solution was maintained in blowcase 11 at 76 C. and pumped by the high temperature type jacketed metering pump 14 through a sand bed filter 15 and a heated tube 16, whose temperature was 160 C., to a spinneret 18 having 100 orifices of a diameter of 0.08 mm. The continuously extruded filaments were withdrawn at 30 meters per minute downward through spinning cell 20 which in this case was 20 feet in length and after being passed over rolls 41 and 42 were wound directly onto a bobbin, not shown, by a conventional winding device. In this operation the bottom of the cell was jacketed at 240 C. and the top /3 was jacketed at 70 C. Heated air was passed through the cell during spinning as follows: 4.9 C. F. M. at 198 C. was blown from jet 36 across the filaments and 7.0 C. F. M. at 240 C. was blown into the bottom of the cell chamber 24 through pipes 26 and 27. All of the air was withdrawn from cell chamber 24 through pipes 37 and 38. The other inlet and outlet pipes shown in Fig. 1 were suitably closed by valves, not shown, during this operation.

The yarn wound on the packages was found to possess the following characteristics: 785 denier, 0.66 gram per denier dry test and 7.4% stretch. The yarn contained 2.0% residual solvent.

Example 2 A spinning solution was prepared consisting of 18% of an acrylonitrile polymer having an average molecular weight of 49,500 dissolved in dimethyl formarnide solvent to give a solution having a viscosity of 570 poises at 100 C. This solution was conducted to apparatus resembling that shown in Fig. 1 through pipe 10 to blow case 11 and then pumped with jacketed metering pump 14 through the filter 15 and heated tube 16 and a sand filter spinneret 18 having 30 orifices 0.10 mm. in diameter. The solution temperature was C. The extruded filaments were withdrawn at 100 meters per minute downward through the spinning cell 20 which in this case was 30 feet long, and after passing around rolls 41 and 42 was wound directly onto a bobbin. The top third of the spinning cell was jacketed at 93 C., the bottom third at 280 C., and the middle third section at 220 C. Heated air was passed into the cell during spinning as follows: 6.5 C. F. M. at 218 C. from jet 36 across the face of the spinneret, 15 C. F. M. at 220 C. through pipes 31 and 32 in at the middle section of the cell, and 10 C. F. M. at 280 C. through pipes 26 and 27 at the bottom of the cell. Air was withdrawn from the cell as follows: 12.5 C. F. M. from the top of the cell through pipes 37 and 38; 5 C. F. M. /3 of the way down the cell through pipes 33 and 34, and 15 C. F. M. /3 of the way down the cell through pipes 28 and 29.

The yarn was tested and found to have the following properties: 480 denier, dry test 0.65 gram per denier and 7.8% stretch. The yarn contained 5.1% residual dimethyl formamide solvent.

Example 3 A spinning solution was prepared as in Example 2 and extruded in the same manner. The extruded filaments were withdrawn at 120 meters per minute downward through a spinning cell of the type shown in Fig. 1, but thirty feet long, and passed around roll 41 and 42 at 120 meters per minute; thence A of a turn around roll 43 which is heated to 160 C. and surrounded partially by shoe 44 which is heated to 350 C. and thence to double rolls 45 and 46 which are each traveling at 240 meters per minute. After three Wraps around the rolls 45 and 46 the yarn continues to godet roll 47 which is rotated at the same rate as the pair of rolls 45 and 46. From roll 47 the yarn may proceed to a ring winder for winding the yarn on a bobbin, not shown. During the spinning, the walls of spinning cell 20 were maintained at the following temperatures: the top /3 was maintained at 99 C., the middle /3 at 220 C., and the bottom /3 at 300 C. Air was passed into the cell as follows: 5.5 C. F. M. at 246 C. across the face of the spinneret, 15 C. F. M. at 220 C. at the middle of the cell, and C. F. M. at 300 C. at the bottom of the cell. Air was withdrawn as follows: 12.5 C. F. M. near the top, 5 C. F. M. /3 down from the top, and C. F. M. down from the top.

The yarn wound on the bobbin had been drafted at at ratio of 2/1 and possessed properties as follows: 153 denier, dry test 1.80 grams per denier and 13.2% stretch.

The yarn was subsequently drafted with hot roll and shoe methods at a ratio of 3.0/1 and found to have the following properties: 56 denier, 4.07 grams per denier and 14.0% stretch on dry test. The yarn contained 0.8% residual solvent. Suitable apparatus and process for drafting and relaxing the yarn is disclosed in a copending application S. N. 329,966, filed of even date in the names of Head, Keik and Mather and entitled Method of Treating Yarns and Filaments and Products Produced Thereby.

Example 4 A spinning solution was prepared consisting of 25% of an acrylonitrile N-rnethyl methacrylamide graft polymer (18% modifier) with an average molecular weight of 46,300 dissolved in dimethyl formamide to give a spinning solution having a viscosity of 768 poises at 100 C. This solution was maintained in the blowcase at 78 C. and pumped by the high temperature type metering pump through a tube heated at160 C. to a spinneret having sixty orifices 0.08 mm. in diameter. The extruded filaments were withdrawn at 50 meters per minute downward through a spinning cell, like that shown in Fig. 1, twenty feet long, and around a roll to a ring winder and wound on a bobbin. The bottom of the cell was jacketed at 240 C. and the top V6 at 70 C. Heated air was passed through the cell as follows: 3.8 C. F. M. at 198 C. across the face of the spinneret and 7.0 C. F. M. at 240 C. in at the bottom. All of the air was withdrawn near the top of the cell. The yarn wound on packages was found to be 625 denier and tested 1.11 grams per denier, with 4.0% dry stretch.

After subsequent drafting at a ratio of 6.4/1 with hot roll and shoe drafting methods and relaxing, this same yarn was tested 116 denier and 3.12 grams per denier and 26.4% dry stretch. This yarn contained 5.7% residual solvent.

Example 5 A spinning solution was prepared consisting of 25% of an acrylonitrile N-methyl methacrylamide graft polymet (18% modifier) having an average molecular weight of 47,600 dissolved in dimethyl formamide solvent to give a solution having a viscosity of 840 poises at 100 C. This solution was maintained at 66 C. in a solution system and pumped by a delivery pump and metering pump through a cotton flannel cloth filter at 66 C. and through the heated tube at 140 C. to a spinneret having sixty orifices 0.10 mm. in diameter. The extruded filaments were withdrawn at meters per minute downward through the spinning cell 20 and around the roll 41 and 42 to the hot roll 43 and thence to rolls 45 and 46, the godet roll 47 and to the windup, not shown. The yarn take up speed of the pair of rolls was 240 meters per minute to give a draft ratio of 3 to 1 between roll 43 and the rolls 45 and 46. The top Va of the spinning cell 20 was jacketed at 140 C., the middle 16 at 220 C. and the bottom Va at 300 C. Heated air was passed into cell chamber 24 as follows: 4.5 C. F. M. at 300 C. at the top across the face of the spinneret, 15 C. F. M. at 220 C. at the middle of the cell, and 10 C. F. M. at 300 C. at the bottom of the cell. Air was withdrawn as follows: 10.5 C. F. M. near the top of the cell, and 19 C. F. M. of the way down the cell from the top. The yarn wound on packages was found to test as follows: 275 denier, 2.10 grams per denier and 15.4% dry stretch. The yarn contained 1.9% residual solvent.

Example 6 A spinning solution was prepared consisting of 25 of an acrylonitrile and N-isopropyl acrylamide graft polymer (25% modifier) having an average molecular weight of 48,400 dissolved in dimethyl formamide solvent to give a solution having a viscosity of 432 poises at C. This solution was maintained at 80 C. in the blowcase and pumped by a high temperature metering pump through the heated tube at C. and a sand filter to a spinncret having thirty orifices each of 0.10 mm. in diameter. The extruded filaments were withdrawn at 120 meters per minute downward through a spinning cell thirty feet in length and around the roll, cot, heated roll, the pair of draw rolls, and godet roll to a bobbin windup as in Example 3. The speed of the pair of draw rolls was 240 meters per minute giving a draft ratio of 2/l. The top /3 of the spinning cell was jacketed at 240 C., the middle Va at 220 C., and the bottom /3 at 270 C. Heated air was passed into the cell as follows: 5.5 C. F. M. at 350 C. in at the top and directed across the face of the spinneret, 15 C. F. M. at 220 C. in at the middle of the cell and 10 C. F. M. at 280 C. in at the bottom of the cell. Air was withdrawn as follows: 10.5 C. F. M. near the top of the spinning cell, 5 C. F. M. /3 of the way down the cell, and 15 C. F. M. 2/ 3 of the Way down the cell. The yarn wound on packages was found to test as follows: 165 denier, 1.27 grams per denier and 16.8% dry stretch. The yarn was later heated and stretched four times its length and it tested as follows: 46.5 denier, 3.51 grams per denier and 19.8% stretch. The yarn contained 2.9% residual dimethyl formamidc solvent.

Example 7 A spinning solution was prepared consisting of 18.5% of an acrylonitrile polymer with an average molecular weight of 51,000 dissolved in dimethyl formamide solvent to give a solution having a viscosity of 342 poises at 100 C. This solution was maintained at 80 C. in the blowcase and pumped by a high temperature type jacketed metering pump through a heated tube at C. and a sand filter to a spinneret having 100 orifices of 0.08 mm. in diameter. The extruded filaments were withdrawn at 65 meters per minute downward through a spinning cell thirty feet long. The spinning cell was jacketed as follows: 140 C. for the top /3, 220 C. for the middle /3 and 280 C. for the bottom /s. Air was passed into the cell as follows: 3.0 C. F. M. at 390 C. at the top across the face of the spinneret, 15 C. F. M. at 220 C. at the middle, and 10 C. F. M. at 280 C. at the bottom,

Air was withdrawn at the rate of 10.5 C. F. M. near the top, 2.5 C. F. M. /a of the way down, and C. F. 2/ 3 of the day down the cell. The yarn at 1080 denier was withdrawn at 65 meters per minute at the bottom of the cell and passed around the draw out roll 41 and idler cot 42 to a hot roll 50 traveling at the same surface speed as roll 41. The hot roll was maintained at 160 C. and was partially surrounded by a hot shoe at 350 C. The yarn passed from the hot roll 43 to the pair of rolls 4S and 46 both of which travel at 260 meters per minute surface speed. These rolls 45 and 46 are skewed so as to advance the yarn with each wrap. The yarn traveled three wraps around rolls 45 and 46 and around the godet roll 47 placed at right angles to them. The yarn was passed through a crimper, through a tow drier for drying and relaxing of the yarn, and to a cutter for cutting the yarn into staple fibers. The staple fibers comprised three denier per filament staple being 2 inches in length. The staple was subsequently processed into spun yarn. This spun yarn tested as follows: 19s cotton count, 1.52 grams per denier and 14.0% stretch. The yarn contained approximately 0.66% residual solvent. The yarn had no shrinkage in hot water after processing.

Example 8 A spinning solution was prepared and extruded as in Example 7. The extruded filaments were withdrawn downward through a spinning cell maintained at the conditions described in Example 7. The yarn was withdrawn at the bottom of the spinning cell at 45 meters per minute and treated on the apparatus shown in Fig. 2. The yarn was passed around hot roll 50 where it is heated by that roll and by shoe 51 and to the pair of rolls 52 and 53 which are driven so as to give a draft ratio of 6.0/1. The yarn was then passed over a second hot roll 54 partly surrounded by a hot shoe 55 and driven at a slower speed so as to allow the yarn to shrink or relax and to another pair of rolls 56 and 57 driven at such a speed that the yarn leaving the hot roll 55 was under only a slight tension. The temperature of rolls 50 and 54 was 200 C., the adjacent shoes 51 and 55 350 C. respectively. The yarn was then crimped, dried, and cut for staple as 2" staple, 3 denier per filament. The staple was subsequently processed into spun yarn and tested as follows: 19s cotton count, 1.87 grams per denier and 12.2% stretch. The yarn contained 0.67% residual solvent. The processed yarn had no hot water shrinkage.

Example 9 A spinning solution was prepared consisting of 19.5% of an acrylonitrile polymer with an average molecular weight of 51,000 dissolved in dimethyl formamide solvent to give a solution having a viscosity of 300 poises at 100 C. This solution was maintained at 78 C. in a storage tank and pumped by means of a delivery pump and a metering pump through a flannel cloth filter at 78 C. and a heated tube at 150 C. to a spinneret having 200 orifices 0.10 mm. in diameter. The extruded filaments were withdrawn downward through a spinning cell thirty feet in length. The spinning cell was jacketed at 140 C. for the top 1/3, 220 C. for the middle Va, and 280 C. for the bottom V3. Heated air was passed into the cell as follows: 5.5 C. F. M. at 370 C. at the top directed across the spinneret face, 35 C. F. M. at 220 C. at the center of the cell, and 40 C. F. M. at 280 C. at the bottom of the cell. Air was withdrawn from the cell as follows: 35 C. F. M. near the top of the cell, 24 C. F. M. 1 down from the top, and 23.5 C. F. M. Vi up from the bottom. The yarn was withdrawn at the bottom of the cell at 3460 deniers at 80 meters per minute and treated as shown in Fig. 2. The yarn was conducted around the draw-out roll and idler cot and around a hot roll traveling at the same speed. The yarn then passed to the pair of rolls to be wound up at a speed to give a draft ratio of 5/1 and around the second hot roll and to a slower rotating pair of rolls to permit the yarn to relax and thence to a suitable windup. The yarn was tested and found to be 735 denier with 2.38 grams per denier and 15.2% stretch. The yarn was found to contain 3.7% residual solvent. The yarn had 1.8% hot water shrinkage.

Example 10 A spinning solution was prepared consisting of 23.5% of an acrylonitrile and N-methyl methacrylamide graft polymer (18% modifier) having an average molecular weight of 48,700 dissolved in dimethyl formamide solvent to give a solution having a viscosity of 900 poises at 100 C. This solution was maintained at 70 C. in a storage tank and pumped by means of a delivery and metering pump through a flannel cloth filter at 70 C. and through a hot tube heated at 140 C. to a spinneret having 150 orifices each 0.10 mm. in diameter. The extruded filaments were withdrawn downward through a spinning cell thirty feet in length. The spinning cell was jacketed at 140 C. for the top /3, 220 C. for the middle .6, and 300 C. for the bottom /3. Heated air was passed into the cell as follows: 5.5 C. F. M. at the top of the cell directed across the face of the spinneret, 20 C. F. M. at the center of the cell, and 15 C. F. M. at the bottom of the cell. Air was withdrawn as follows: 15.5 C. F. M. near the top of the cell, and 25 C. F. M. Va of the way up from the bottom of the cell. The yarn with withdrawn from the bottom of the cell at 227 denier at meters per minute around a roll and idler cot and then around a hot roll to the pair of drafting rolls traveling at higher speed to give the yarn a draft ratio of 60/1. The yarn then passed around another hot roll and to a second pair of double rolls driven so as to permit the yarn to relax. The yarn then passed through a crimper and cutter to make three inch, three denier per filament staple fiber. Spun staple yarn processed from this staple tested 1.66 grams per denier and 16.6% stretch. The yarn contained 3.45% residual solvent. The yarn had no hot water shrinkage after processing.

Example 11 A spinning solution was prepared consisting of 23% of an acrylonitrile and N-methyl methacrylamide graft polymer (18% modifier) having an average molecular weight of 47,600 dissolved in dimethyl formamide solvent to give a solution having a viscosity of 840 poises at C. This solution was maintained at 70 C. in a storage tank and pumped by means of pumps to a spinneret at the same conditions described in Example 10. The yarn was withdrawn through a spinning cell at the same conditions as in Example 10 except that it was withdrawn at 1176 denier and 160 meters per minute. The heated rolls and pairs of rolls were operated at the same conditions as in Example 10 with the exception that all of the speeds were doubled. The yarn tow after drafting and relaxing, before crimping and cutting tested 2.34 grams per denier and 24.2% dry stretch. The yarn contained 3.0% residual solvent. The yarn had 0.6% residual hot water shrinkage.

Example 12 {8. spinning solution was prepared as in Example 11. This solution was maintained at 58 C. in a storage tank and pumped by means of a delivery pump and metering pump through a heated tube at C. to a spinneret having orifices each 0.10 mm. in diameter. The yarn was withdrawn downward through a spinning cell 30 feet in length and jacketed as follows: 140 C. for the top Va, 220 C. for the middle A and 290 C. for the bottom 56. Air was blown into the cell as follows:

5.5 C. F. M. at 310 C. at the top across the face of the spinneret, C. F. M. at 220 C. at the middle of the cell, and 10 C. F. M. at 290 C. at the bottom of the cell. Air was withdrawn as follows: 10.5 C. F. M. near the top of the cell and C. F. M. up from the bottom of the cell. The yarn was withdrawn at 2160 denier at 50 meters per minute at the bottom of the cell and after passing over a roll and idler cot and a hot roll at 210 C. surrounded by a shoe at 360 C. was passed through wraps around the pair of rolls traveling at 300 meters per minute to give a draft ratio of 6.0/1. The yarn was then passed around the second hot roll and shoe for relaxing and thence Wound with a ring winder. The yarn properties tested as follows: 415 denier, 2.89 grams per denier and 19.2% stretch. The yarn contained 1.4% residual solvent.

Example 13 A spinning solution was prepared consisting of of an acrylonitrile and N-isopropyl acrylamide graft polymer (25% modifier) having an average molecular Weight of 49,800 dissolved in dimethyl formamide solvent to give a solution having a viscosity of 456 pulses at 100 C. This solution was maintained at 80 C. in a blowcase and pumped by means of a metering pump through a flannel cloth filter at 80 C. and through a heated tube at 140 C. to a spinneret having 60 orifices each 0.10 mm. in diameter. The yarn was withdrawn downward through a spinning cell thirty feet in length and jacketed as follows: 140 C. for the top Vs, 220 C. for the middle /3 and 280 C. for the bottom /3. Air was blown into the cell as follows: 4.5 C. F. M. at 180 C. at the top across the face of the spinneret, 15 C. F. M. at 220 C. at the center of the cell, and 10 C. F. M. at 280 C. at the bottom of the cell. Air was withdrawn as follows: 10.5 C. F. M. out near the top of the cell and 19 C. F. M. out /3 of the way down the cell. The yarn was withdrawn at the bottom of the cell at 50 meters per minute by a roll and idler cot and passed around the hot rolls for drafting and relaxing. The draft ratio was kept at 6.0 and yarn properties after relaxing were tested as follows: 2.58 grams per denier, 22.1% stretch and 0.0% but water shrinkage. This yarn was processed into staple spun yarn. The yarn as originally spun contained 1.1% residual solvent.

Variations within the scope of the invention include use of solvents other than dimethyl formamide such as dimethyl acetamide and N-butyryl lactone. Methods of metering and filtering the spinning solution prior to extrusion may also be somewhat modified. It will be understood that the heated rolls and heated shoes may be heated by any conventional manner such as by electricity, hot oil, hot gas or by internal flames.

For successful operation, it is necessary that the spinning solution have a solids content of at least 18% and a viscosity not less than 400 poises at 100 C. The stream of air blown across the spinneret face should be maintained in the temperature range of 150 C.-400 C. It is further essential that the walls of the spinning cell surrounding the spinneret and continuing down to a distance 10 feet below the spinneret be maintained at some temperature not more than 200 C. It is further essential that the spinning cell wall temperature in the lower section be so adjusted as to leave not more than 5% residual solvent in the filaments as they issue from the bottom of the spinning cell. The center section should be heated not more than 300 C. and the bottom section not more than 400 C. It is also essential that the heated roll surface temperature and the temperature of the filaments be closely maintained at such a temperature as to permit the filaments to draft and relax freely, yet not cause the filaments to stick to each other or the heated rolls. This temperature is highly variable and depends on the type of polymer being spun, the spinning speeds and filament diameter.

This invention has the advantage of producing high quality fibers directly as contrasted to other processes which involve two or more separate operations, it being necessary to package the yarn between each separate stage. The intermediate packaging of yarn is highly undesirable because of increased labor cost, yarn damage and yarn waste.

We claim:

1. The method of forming yarn from a spinning solution containing in dimethyl formarnide at least 18% of a polymer selected from the group consisting of polyacrylonitrile, a graft polymer of acrylonitrile and N-methylmethacrylamide containing 18% of the latter compound, a graft polymer of acrylonitrile and N-isopropyl acrylamide containing 18% of the latter compound which comprises heating the solution to a temperature within the range of l00l70 C., continuously extruding the hot solution through a spinneret into a spinning cell to form filaments, blowing gas heated to a temperature within the range of 150 to 400 C. across the filaments adjacent the face of the spinneret, drying the filaments by conducting the filaments first through a first section of the spinning cell maintained at a temperature within the range of 70 to 200 C., then conducting the filaments secondly through a second section of the spinning cell maintained at a temperature within the range of 150-300 C., then conducting the filaments through a third section of the spinning cell maintained at a temperature of 250-400 C., the temperature of the second cell section being higher than the first and that of the third higher than the second, continuously drawing the dried filaments from the third cell section at a rate within the range of 30 to 160 meters per minute, heating the filaments to a thermoplastic condition and winding the filaments into a package.

2. The method of forming yarn from a spinning solution containing in dimelhyl formamide at least 18% of a polymer selected from the group consisting of polyacrylonitrile, a graft polymer of acrylonitrile and N-methylmethacrylamide containing 18% of the latter compound, a graft polymer of acrylonitrile and N-isopropyl acrylamide Containing 18% of the latter compound which comprises heating the solution to a temperature Within the range of 170 C., continuously extruding the hot solution through a spinneret into a spinning cell to form filaments, blowing gas heated to a temperature within the range of to 400 C. across the filaments adjacent the face of the spinneret, drying the filaments by conducting the filaments first through a first section of the spinning cell maintained at a temperature within the range of 70 to 200 C., then conducting the filaments secondly through a second section of the spinning cell maintained at a temperature within the range of 150-300 C., then conducting the filaments through a third section of the spinning cell maintained at a temperature of 250400 C., the temperature of the second cell section being higher than the first and that of the third higher than the second, continuously drawing the dried filaments from the third cell section at a rate within the range of 30 to meters per minute, heating the filaments to thermoplasticity but below their sticking point, stretching the heated filaments in a range of from 100 to 600%, further heating the stretched filaments to thermoplasticity while under a tension permitting them to relax in length and winding the filaments into a package.

3. The method of forming yarn from a spinning solution containing in dimethylformarnide 20 to 30% of a graft polymer of acrylonitrile and N-methylmethacrylamide containing 18% of the latter compound which comprises heating the solution to a temperature within the range of i00170 C., continuously extruding the hot solution through a spinneret into a spinning cell to form filaments, blowing gas heated to a temperature within the range of 150 to 400 C. across the filaments adjacent the face of the spinneret, drying the filaments by conducting the filaments first through a first section of the spinning cell maintained at a temperature within the range of 70 to 200 C., then conducting the filaments secondly through a second section of the spinning cell maintained at a temperature within the range of 150-300 C., then conducting the filaments through a third section of the spinning cell maintained at a temperature of 250-400 C., the temperature of the second cell section being higher than the first and that of the third higher than the second, continuously drawing the dried filaments from the third cell section at a rate within the range of 30 to 160 meters per minute, heating the filaments to thermoplasticity but below their sticking point, stretching the heated filaments in a range of from 100 to 600% further heating the stretched filaments to thermoplasticity while under a tension permitting them to relax in length and winding the filaments into a package.

4. The method of forming yarn from a spinning solution containing in dimethylformamide to of a graft polymer of acrylonitrile and N-isopropyl acrylamide containing l8% of the latter compound which comprises heating the solution to a temperature within the range of -170" C., continuously extruding the hot solution through a spinneret into a spinning cell to form filaments, blowing gas heated to a temperature within the range of to 400 C. across the filaments adjacent the face of the spinneret, drying the filaments by conducting the filaments first through a first section of the spinning cell maintained at a temperature within the range of 70 to 200 C., then conducting the filaments secondly through a second section of the spinning cell maintained at a temperature within the range of ISO-300 C., then conducting the filaments through a third section of the spinning cell maintained at a temperature of 250-400 C., the temperature of the second cell section being higher than the first and that of the third higher than the second, continuously drawing the dried filaments from the third cell section at a rate within the range of 30 to meters per minute heating the filaments t0 thermoplasticity but below their sticking point, stretching the heated filaments in a range of from 100 to 600% further heating the stretched filaments to thermoplasticity while under a tension permitting them to relax in length and winding the filaments into a package.

References Cited in the file of this patent UNITED STATES PATENTS l,952,877 Mancini Mar. 27, 1934 2,252,689 Bradshaw Aug. 19, 1941 2,362,063 Fryer Nov. 7, 1944 2,366,275 McComb Jan. 2, 1945 2,404,714 Latham July 23, 1946 2,697,251 Bauer Dec. 2], 1954 OTHER REFERENCES Serial No. 362,260, Egger (A. P. C.), published April 27, 1943. 

1. THE METHOD OF FORMING YARN FROM A SPINNING SOLUTION CONTAINING IN DIMETHYL FORMAMIDE AT LEAST 18% OF A POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYACRYLONITRILE, A GRAFT POLYMER OF ACRYLONITRILE AND N-METHYLMETHACRYLAMIDE CONTAINING 18% OF THE LATTER COMPOUND, A GRAFT POLYMER OF ACRYLONITRILE A N-ISOPROPYL ACRYLAMIDE CONTAINING 18% OF THE LATTER COMPOUND WHICH COMPRISES HEATING THE SOLUTION TO A TEMPERATURE WITHIN THE RANGE OF 100-170*C., CONTINUOUSLY EXTRUDING THE HOT SOLUTION THROUGH A SPINNERET INTO A SPINNING CELL TO FORM FILAMNETS, BLOWING GAS HEATED TO A TEMPERATURE WITHIN THE RANGE OF 150 TO 400*C. ACROSS THE FILAMENTS ADJACENT THE FACE OF THE SPINNERET, DRYING THE FILAMENTS BY CONDUCTCELL MAINTAINED AT A TEMPERATURE WITHIN THE RANGE OF 70 TO 200*C., THEN CONDUCTING THE FILAMENTS SECONDLY THROUGH A SECOND SECTION OF THE SPINNING CELL MAINTAINED 